1. Field of the Invention
Aspects of the present invention relate to a power management method, and more particularly, to an adaptive power management method in a portable electronic device, in which power consumed in a main module such as a central processing unit (CPU) is saved by adjusting an operational clock frequency of the CPU according to a use state in the portable electronic device.
2. Description of the Related Art
Recently, MP3 players allowing users to conveniently listen to music by storing audio and music files in a memory and Portable Multimedia Players (PMPs) allowing users to view a moving picture by means of a display unit by storing video files have been developed, and portable terminals having an MP3 function, an PMP function, and a digital camera function are available on the market.
With these portable electronic devices, there has been a trend towards combining the various functions. However, because of size and weight limitations, batteries that are used with portable electronic devices typically have a limited capacity, even when fully charged. Accordingly, the development of portable electronic devices that can perform various functions while simultaneously maintaining a long battery life between recharging has become important for user convenience.
For the portable electronic devices, a power management method for controlling a CPU clock frequency to efficiently use available battery capacity has been developed. CPUs of portable electronic devices are limited in terms of their operational clock frequency, since as the CPU clock frequency increases, the power consumption in the CPU increases, thereby reducing the battery life. Thus, portable electronic devices need to maintain an optimal CPU clock frequency according to an operational state.
For example, when a moving picture is reproduced, the CPU of an electronic device having a function of reproducing video and music typically must maintain the maximum clock frequency in order to run the video reproduction application without any problem. However, when only music files, such as MP3 files, are reproduced while a display unit such as a Liquid Crystal Display (LCD) is in an “off” state, the maximum clock frequency is not needed, and the power consumption of the electronic device can be reduced by decreasing the clock frequency to a predetermined value suitable for reproducing only music files.
FIG. 1 is a diagram of a portable electronic device utilizing a conventional power management method for power management. In the power management software configuration illustrated in FIG. 1, a user interface state 18 of a multi-functional device such as, for example, a multi-function MP3 player, can be classified into a power “on” state, a power “off” state, an idle state, and a normal state. The normal state can be classified into sub-states 19 indicating states for performing, for example, an audio function, an image function, frequency modulation (FM), universal serial bus (USB), and an encoding function.
A reception module 10 receives information on each sub-state indicating an audio, image, FM, reproduction, or image reproduction setting state from the user interface 18 and separately stores the information. An analysis module 12 analyzes the information and transmits the analysis result to an adaptation module 14. The adaptation module 14 calculates an operational clock frequency for the CPU using a lookup table 16 and adding the clock frequency for the power level corresponding to the setting state of each sub-state.
The power level for each of the audio, image, USB, and encoding modes and the power level for each of the audio effects and LCD on/off modes are independently defined. In order to determine the power level when an MP3 player performs multi-tasking for processing audio and images at the same time or when the MP3 player adds an audio effect function to audio reproduction, the clock frequencies of the power levels are simply set according to relevant modes determined in advance and are added together without any condition. Therefore, power may be unnecessarily wasted.
For example, if a processing speed of 30 million instructions per second (MIPS) is required to reproduce an MP3 file and a processing speed of 20 MIPS is required to perform a Digital Natural Sound engine (DNSe) audio effect, in the conventional power management method, if these two functions are used at the same time, a CPU clock frequency corresponding to 50 MIPS is calculated by simply adding the processing speeds corresponding to the two selected functions. However, if these two functions are capable of working together with a CPU clock frequency corresponding to only 40 MIPS, the CPU clock frequency calculated by the above method is 10 MIPS higher than it needs to be, and excessive power consumption occurs.